1. Field of the Invention
The present invention relates to a CDMA mobile communications system and its random access control method and base station. More particularly, it relates to a CDMA mobile communications system that allows a plurality of mobile stations to access a base station at any time using a common channel, and has the base station control the message transmission of the mobile stations, and its random access control method and base station.
2. Description of Related Art
In a random access control method of a conventional CDMA mobile communications system, a mobile station which tries to make a call transmits a preamble notifying a base station of occurrence of a message, and the base station that receives the preamble compares the output of a matched filter with a predetermine threshold value, and transmits a transmission control signal for controlling the message transmission of the mobile stations in response to the compared result. The output of a matched filter, however, has a plurality of peaks because of the signal power dispersion due to delay spread on a transmission path. As a result, the probability of missing the preamble increases when comparing the peak values with the threshold value.
In this way, the random access control method of the conventional CDMA mobile communication makes a decision on whether to authorize the message transmission or not by comparing the output of a matched filter with the threshold value. In other words, it makes a decision in the condition of the signal power dispersion, which offers a problem of increasing a chance of missing the preamble.